1. Field of the Invention
The present invention relates to a thin-film device incorporating a conductor layer and a terminal electrode connected to the conductor layer.
2. Description of the Related Art
With increasing demands for reductions in dimensions and thickness of high frequency electronic apparatuses such as cellular phones, reductions in dimensions and profile of electronic components mounted on the high frequency electronic apparatuses have been sought. Some of the electronic components have such a configuration that insulating layers and conductor layers are formed on a substrate through the use of thin-film forming techniques. Such electronic components formed through the use of thin-film forming techniques are called thin-film device in the present patent application.
In a thin-film device, terminal electrodes are provided for connecting conductor layers to an external circuit. Here, a portion of the thin-film device other than the terminal electrodes is called a device main body. Each conductor layer connected to the terminal electrodes includes a wiring portion, for example, and is formed so that an end face of the wiring portion is exposed at a side surface of the device main body. In this case, the terminal electrodes are disposed on the side surfaces of the device main body, for example, so as to be connected to the end faces of the wiring portion.
Here is given an example of a method of manufacturing a thin-film device wherein the terminal electrodes are disposed on the side surfaces of the device main body. In the method, first, a thin-film device substructure is fabricated by forming layers such as conductor layers corresponding to a plurality of thin-film devices on a single wafer (a substrate). The substructure includes a plurality of preliminary device main body portions each of which will be a device main body. Furthermore, in the substructure, there are provided portions to be removed between respective adjacent ones of the preliminary device main body portions. Next, the plurality of preliminary device main body portions are divided into a plurality of device main bodies by cutting the substructure at positions of the portions to be removed. By cutting the substructure in such a manner, side surfaces of the device main bodies are formed, and end faces of wiring portions to be connected to terminal electrodes are exposed at the side surfaces. Next, the terminal electrodes are formed on the side surfaces of the device main bodies.
To reduce the dimensions and profile of a thin-film device, it is effective to reduce the thickness of layers such as conductor layers. However, according to the above-described method, a reduction in thickness of conductor layers causes a reduction in area of the end faces of the wiring portion connected to the terminal electrodes. As a result, the regions in which the conductor layers touch the terminal electrodes are reduced in area, and accordingly it becomes difficult to secure the reliability of connection between the conductor layers and the terminal electrodes.
To avoid this problem, such a technique is conceivable that the wiring portion may be increased in width to thereby increase the area of the end faces of the wiring portion. However, this may cause a problem in the thin-film device that the density of the wiring portion is reduced and therefore it becomes difficult to reduce the dimensions of the thin-film device, or that the impedance of the wiring portion deviates from a desired value and the characteristics of the thin-film device are thereby degraded.
JP 10-163002A discloses a technique wherein, in a chip-shaped electronic component in which an inner conductor film is disposed on a substrate and external terminal electrodes are connected to end faces of the inner conductor film, the end faces of the inner conductor film are tilted with respect to a sectional surface of the substrate.
JP 11-003833A discloses a technique wherein, in an electronic component in which electrodes are disposed on a substrate and external terminals are connected to end faces of the electrodes, the end faces of the electrodes on the substrate are tilted with respect to a sectional surface of the substrate.
JP 4-037105A discloses a thin-film capacitor wherein: there are stacked on a substrate a pair of inner electrode layers, a dielectric layer disposed between the pair of inner electrode layers, and a protection film covering the inner electrode layers and the dielectric layer; and outer electrode layers connected to the inner electrode layers are disposed on side surfaces of the substrate. JP 4-037105A discloses a technique wherein portions of the top surfaces of the inner electrode layers near the side surfaces of the substrate are exposed instead of being covered with the protection film, and the outer electrode layers are connected to the end faces and the portions of the top surfaces of the inner electrode layers.
JP 2-121313A discloses a thin-film capacitor wherein: three or more inner electrode layers and two or more dielectric layers are alternately stacked on a substrate; the inner electrode layers and the dielectric layers are covered with a protection film; and outer electrodes connected to the inner electrode layers are disposed on side surfaces of the substrate. JP 2-121313A discloses a technique wherein portions of the top surfaces of the inner electrode layers near the side surfaces of the substrate are exposed instead of being covered with the protection film, and the outer electrodes are connected to the end faces and the portions of the top surfaces of the inner electrode layers.
JP 5-129149A discloses a thin-film capacitor wherein: four inner electrodes and four dielectric thin films are alternately stacked on a substrate; the inner electrodes and the dielectric thin films are covered with an inorganic insulating film and a resin layer; and outer electrodes connected to the inner electrodes are disposed on side surfaces of the substrate. JP 5-129149A discloses a technique wherein portions of the top surfaces of the inner electrodes near the side surfaces of the substrate are exposed instead of being covered with the inorganic insulating film and the resin layer, and the outer electrodes are connected to the end faces and the portions of the top surfaces of the inner electrodes.
In the following description the external terminal electrodes of JP 10-163002A, the external terminals of JP 11-003833A, the external electrode layers of JP 4-037105A, and the external electrodes of JP 2-121313A and JP 5-129149A are all called terminal electrodes.
As previously described, in a thin-film device in which terminal electrodes are disposed on the side surfaces of the device main body, a reduction in thickness of conductor layers causes a reduction in area of the end faces of the wiring portion connected to the terminal electrodes, and as a result, the regions in which the conductor layers touch the terminal electrodes are reduced in area and accordingly it becomes difficult to secure the reliability of connection between the conductor layers and the terminal electrodes.
According to the techniques disclosed in the two publications of JP 10-163002A and JP 11-003833A, it is possible to increase the area of the regions in which the conductor layers touch the terminal electrodes, but the amount of increase in the area is very small. It is therefore difficult to secure a satisfactory degree of reliability of connection between the conductor layers and the terminal electrodes through the use of the techniques disclosed in these two publications.
According to the techniques disclosed in the three publications of JP 4-037105A, JP 2-121313A and JP 5-129149A, it is possible to greatly increase the areas of the regions in which the conductor layers touch the terminal electrodes, compared with the case in which the terminal electrodes touch only the end faces of the conductor layers. However, the following problems arise if the techniques disclosed in these three publications are applied to thin-film devices in general. According to the techniques disclosed in the three publications, it is difficult to precisely control the shapes and locations of the terminal electrodes, which results in increases in variations in shapes and locations of the terminal electrodes among products. If such variations among products occur, there is a possibility that variations may occur in magnitude of electromagnetic coupling or capacitive coupling between the conductor layers and the terminal electrodes, and electrical characteristics of the thin-film devices may vary. Furthermore, in the case in which the number of terminal electrodes is large, in particular, if there occur variations in shapes and locations of the terminal electrodes among products, variations in distance between the respective adjacent ones of the terminal electrodes occur, which results in variations in electrical characteristics of the thin-film devices and/or short-circuit between adjacent ones of the terminal electrodes. These problems become more noticeable as the number of the terminal electrodes increases and downsizing of the thin-film devices proceeds.